Policy control in session initiation protocol forking

ABSTRACT

Methods and apparatuses for updating policy and charging rules relating to early dialogs in session initiation protocol forking in a telecommunications network. A node comprises a receiver ( 304 ), configured to receive a plurality of preliminary responses originating from a plurality of terminating end points as part of Session Initiation Protocol, SIP, forking. The node comprises an early dialog controller ( 314 ), configured, for each received preliminary response, to determine a unique identifier and to control a transmitting means, which may be a transmitter ( 302 ), to transmit a corresponding preliminary message comprising the unique identifier to a further node ( 400 ) for use as a Policy and Charging Rules Function, PCRF ( 200 ), for creating an early dialog by the further node. The receiver is further configured to receive updated data for at least one of the preliminary responses. The node further comprises an updated dialog controller ( 316 ) configured to retrieve the unique identifier corresponding to the at least one preliminary response and control the transmitter to transmit an updating message based on the updated data and comprising the retrieved unique identifier to the further node for updating the corresponding early dialog.

PRIORITY

This non-provisional application is a U.S. National Stage Filing under35 U.S.C. § 371 of International Patent Application Serial No.PCT/EP2014/065269 filed Jul. 16, 2014, and entitled “Policy Control inSession Initiation Protocol Forking.”

TECHNICAL FIELD

The invention relates to session initiation protocol forking. Morespecifically, the invention relates to, but is not limited to, updatingpolicy and charging rules relating to early dialogs in sessioninitiation protocol forking.

BACKGROUND

Session Initiation Protocol (SIP) forking is the ability of a SIP proxyserver to fork SIP request messages to multiple destinations accordingto IETF RFC 3261. This allows the Internet Protocol (IP) MultimediaSubsystem (IMS) to send an incoming SIP request addressed to a PublicUser Identity to multiple terminating end points when multiple contactaddresses have been registered for the same Public User Identity.

Support for SIP forking in the IMS is specified in 3GPP TS 23.228, andthe related User Equipment (UE) procedures are described in 3GPP TS24.229. Support for SIP forking when policy control is applied isspecified in 3GPP TS 29.214.

The typical use case is as follows. A connected UE initiates an IMSsession by sending an INVITE request to a Proxy Call Session ControlFunction (P-CSCF). The P-CSCF forwards the INVITE towards a Serving CallSession Control Function (S-CSCF) and then the S-CSCF towards aterminating IMS network. The terminating IMS network sends the requestin parallel to multiple registered contact addresses for the calledparty, creating several early dialogs from a single request. Eachterminating end point sends a preliminary SIP response and, aftersuccessful SDP negotiation, starts ringing. The terminal that answersthe call sends a final 200 OK (for INVITE) response, and thecommunication path is established to this particular end point, whilstall other early dialogs are cancelled or released.

As a result, the originating P-CSCF may receive multiple preliminary SIPresponses due to forking, as multiple early media sessions may beestablished before the final SIP response is received. When policycontrol is applied, a Policy and Charging Rules Function (PCRF) iscontacted for each early media session as it needs to be authorized, andthe allocated resources may need to be updated when subsequentpreliminary responses are received, according to the resources needed byeach early dialog.

Policy control is initiated when the P-CSCF establishes a Diametersession with the PCRF over an Rx reference point as part of theestablishment of a SIP session. This can occur when the originating UEinitiates the SIP request or upon reception of the firstpreliminary/final SIP response for the SIP request. This Diametersession is reused for each subsequent preliminary/final SIP responsereceived as part of the same SIP session in order to provide additionalor modified service information.

The UE and the P-CSCF become aware of the forking only when a subsequentpreliminary SIP response arrives for a new early dialogue.

According to 3GPP TS 29.214, after the first early media session isestablished, for each subsequent preliminary SIP response establishingan additional early media session, the P-CSCF shall use an AA-Request(AAR) message within the existing Diameter session containing theSIP-Forking-Indication Attribute Value Pair (AVP) with the valueSEVERAL_DIALOGUES and include the service information derived from thelatest preliminary SIP response. An AA-Request (AAR) message isacknowledged towards the P-CSCF with an AA-Answer (AAA) message. For thesake of simplicity, AAA messages are neither further commentedthroughout this specification nor illustrated in any drawing.

In addition, the P-CSCF provisions the service information derived fromany subsequent Session Description Protocol (SDP) offer-answer exchangewithin an early dialogue (e.g. in PRACK and 200 OK (PRACK), or UPDATEand 200 OK (UPDATE)) using an AAR message within the existing Diametersession containing the SIP-Forking-Indication AVP with valueSEVERAL_DIALOGUES and the derived service information.

When receiving an AAR message containing the SIP-Forking-Indication AVPwith value SEVERAL_DIALOGUES, the PCRF shall authorize any additionalservice data flow filters, any additional media components and anyincreased Quality of Service (QoS) requirements for the previouslyauthorized media components, as requested within the serviceinformation. The PCRF shall authorize the maximum bandwidth required byany of the dialogues, but not the sum of the bandwidths required by alldialogues. The reason is that there will be early media sent from onlyone of the early dialogs, not from all the early dialogs. The PCRF shallalso open or close the gates for service flows depending on the flowstatus that is being provisioned.

According to 3GPP TS 29.214, the P-CSCF shall store the SDP informationfor each early dialogue separately till a final SIP response isreceived. When the final SIP session is established, all the other earlydialogues are terminated and the service information for the SIP sessionis updated to match the requirements of the remaining early dialogueonly.

When receiving the first preliminary/final SIP response, the P-CSCFsends an AAR message without the SIP-Forking-Indication AVP and includesthe service information derived from the SDP corresponding to thedialogue of the preliminary/final response. The PCRF updates theinstalled Policy Control and Charging (PCC) Rules information andAuthorized-QoS information to match only the requirements of the serviceinformation within this AAR message, and also to open or close the gatesfor service flows according to the flow status in the received serviceinformation.

The Customized Alerting Tones (CAT) service is an IMS terminatingservice that triggers an external Customized Alerting Tones Server(CAT-S) to generate a customized signal (customized welcome message orselected music) towards the caller when the served user is alerted. Theservice allows an end user to define the customized alerting tones to beplayed, and is sometimes called Personal Ring Back Tone.

The Network Provided Ring Back Tone (NRBT) service is an IMS terminatingservice that triggers a Multimedia Resource Function Processor (MRFP) togenerate an NRBT signal (customized welcome message or ringing tone)towards the caller while the served user is alerted. The tone is commonfor all the IMS subscribers and is only configurable by an operator.

A common model to perform the CAT or NRBT service is by using the socalled forking model. This means that an Application Server (AS) in theterminating side (either the Telephony Application Server (TAS) or theCAT-S) is simulating to be a forking leg. Hence, when the 180 Ringingmessage is received from the remote UE, the AS initiates a provisionalearly media session where the customized alerting tone is played.Finally, when the remote UE answers the call, the AS stops the ring backtone and forwards the final answer to establish the communication pathbetween both parties.

Support for the CAT service in IMS is specified in 3GPP TS 24.182.Examples of signalling flows for the CAT service within the IMSsubsystem can be found in 3GPP TS 24.182 Annex A.3

According to 3GPP TS 23.228, QoS-assured preconditions can be negotiatedduring IMS session establishment to ensure that resources are availablein the network before the called subscriber is alerted, thus when thecalled subscriber answers the call the users are guaranteed to be ableto communicate.

The usage of preconditions is strongly recommended as it prevents theproblem of ghost ringing, i.e., that the call appears to be connected,but the users cannot talk with each other.

However, the usage of pre-conditions implies more SIP signaling duringthe session establishment and several invocations from IMS to the packetcore network to update the resources with new session information duringcall establishment.

The Rx Flow-Number AVP, hereinafter referred to as flow identifier, isan ordinal number starting from 1 that identifies the IP flow within themedia component (i.e. it identifies the traffic related to certainservice for certain media, e.g. audio traffic). For a SIP session, theflow identifiers are derived from the SDP information as the ordinalnumber of the position of the “m=” line in the SDP, according to thefollowing rules in 3GPP TS 29.214 Annex B.1.2.

The procedure guarantees that UE and Application Function (AF) assignthe same ordinal number to each media component for a given application.Also, the ordinal number of a media component shall not be changed whenthe session description information is modified.

This means that all multiple preliminary SIP responses due to SIPforking will result in the same flow identifiers being sent from theP-CSCF to the PCRF.

The current support for SIP forking, as specified in 3GPP TS 29.214,does not allow the P-CSCF to modify the session information of aparticular preliminary forking response.

This limitation comes from the fact that all preliminary responses dueto forking make use of the same Diameter Rx session, and theSIP-Forking-Indication AVP can only have the value: SINGLE_DIALOGUE (0),or SEVERAL_DIALOGUES (1). In addition, the flow identifiers (Flow-NumberAVP) derived by the P-CSCF for all preliminary responses overlap, asthey are based on the Session Description Information (SDI) exchangedbetween the AF and the AF session client in the UE.

Hence, the PCRF will identify any AAR message containing theSIP-Forking-Indication AVP with value SEVERAL_DIALOGUES, as a newpreliminary forking response from another terminating end point, when itmay actually be a modification of the session information for a previousforking response. In this situation the PCRF will authorize the receivedservice data flow filters as additional IP flows, when the wantedbehavior is to modify the information provided in the existing PCCrules.

The main disadvantage of the existing solution is that the additional IPflows need to be notified to the UE for policy enforcement in the uplinkpath.

The P-CSCF may need to modify the session information of a preliminaryforking response in the following situations.

-   -   When the P-CSCF provides preliminary service information not        fully negotiated yet (e.g. based on the SDP offer), and then        updates the service information with the SDP answer.    -   If the P-CSCF needs to enable or disable media IP flows        depending on operator policy prior to the completion of the SIP        session set-up, thus allowing or forbidding early media in        forward and/or backward    -   When the SIP terminal makes use of QoS preconditions

FIG 1. shows current support for SIP forking policy control in 3GPP. TheP-CSCF cannot modify the session information of a particular preliminaryforking response, as required in step S-108. Hence, the P-CSCFprovisions the new service information (SDP_b_update) as an additionalearly media session (step S-109). The PCRF believes that this is a newpreliminary SIP response and then modifies the already provided PCCrules to include the service data flow filters provided in the latestAAR message (step S-111).

Since the PCRF believes that it is a new preliminary SIP response, theupdated PCC rule will include the flow information as provided by theP-CSCF, as it is considered that, as it is coming from a differentforking leg, it will be different from the previously providedinformation (different IP address/port from the terminating side).However, if the AAR message is referring to a modification of thesession of an existing forking response where for example only the gatestatus is changed (e.g. enabled media flows are now disabled), the flowinformation has been already provided as part of a PCC Rule to thepacket core network.

Upon reception of an updated PCC rule that contains service data flows,the enforcement point in the network (e.g. Packet Data Network Gateway,PGW) will initiate a bearer update procedure in order to provide the UEwith the service data flows included in the PCC rule. This would createan unnecessary signalling towards the UE, as the terminal is alreadyaware of this filter information.

Different alternatives can be considered in order to solve the problem:

-   -   Impact in the P-CSCF: The P-CSCF can check whether the received        SIP response corresponds to the modification of an existing SIP        dialogue or it refers to a new dialogue. In the first case, the        P-CSCF would have to check, from the SDP data, which information        has been already provided to the PCRF and which information is        different from the already provided one. The P-CSCF would only        provide the updated/new service information.    -   Impact in the PCRF: In order for the PCRF to identify that the        service data flow information is the same than the previously        provided would require that the PCRF checks, for each AAR        command received with the SIP-Forking-Indicator, that the        previously generated PCC rules already installed in the PGW have        the same filter information.    -   Impact in the PGW: in order for the PGW to identify that the        provided filter information has been already provided to the UE,        it would have to retain the previously provided filter        information and check it against the filter information provided        in the PCC Rule.

The three alternatives have a strong performance impact and latencyrequirements that invalidate them as feasible solutions.

SUMMARY

According to the invention in a first aspect, there is provided a nodefor use as a Proxy Call Session Control Function, P-CSCF, in atelecommunications network. The node comprises a receiving means, whichmay be a receiver, configured to receive a plurality of preliminaryresponses originating from a plurality of terminating end points as partof Session Initiation Protocol, SIP, forking. The node comprises anearly dialog controlling means, which may be an early dialog controller,configured, for each received preliminary response, to determine aunique identifier and to control a transmitting means, which may be atransmitter, to transmit a corresponding preliminary message comprisingthe unique identifier to a further node for use as a Policy and ChargingRules Function, PCRF, for creating an early dialog by the further node.The receiver is further configured to receive updated data for at leastone of the preliminary responses. The node further comprises an updateddialog controller configured to retrieve the unique identifiercorresponding to the at least one preliminary response and control thetransmitter to transmit an updating message based on the updated dataand comprising the retrieved unique identifier to the further node forupdating the corresponding early dialog.

Optionally, the early dialog controller is configured to determine theunique identifier by creating said unique identifier or by using a SIPdialog identifier, which is included in the received preliminaryresponse, as a basis for creating said unique identifier.

Optionally, the preliminary message and/or the updating message is anAA-Request, AAR.

Optionally, the early dialog controller is configured to determine theunique identifier as a new attribute value pair, AVP, for adding to theAAR, or to extend an existing AVP of the AAR.

Optionally, the updated data comprises data updating the serviceinformation for at least one early dialog.

According to the invention in a second aspect, there is provided amethod for controlling a node for use as a Proxy Call Session ControlFunction, P-CSCF, in a telecommunications network. The method comprisesreceiving, by a receiving means, which may be a receiver, a plurality ofpreliminary responses originating from a plurality of terminating endpoints as part of Session Initiation Protocol, SIP, forking. The methodcomprises determining, by an early dialog controlling means, which maybe an early dialog controller, for each received preliminary response, aunique identifier. The method comprises controlling, by the early dialogcontroller, a transmitting means, which may be a transmitter, totransmit a corresponding preliminary message comprising the uniqueidentifier to a further node for use as a Policy and Charging RulesFunction, PCRF, for creating an early dialog by the further node. Themethod comprises receiving, by the receiver, updated data for at leastone of the preliminary responses. The method comprises retrieving, by anupdated dialog controller, the unique identifier corresponding to the atleast one preliminary response. The method comprises controlling, by theupdated dialog controller, the transmitter to transmit an updatingmessage based on the updated data and comprising the retrieved uniqueidentifier to the further node for updating the corresponding earlydialog.

Optionally, the method further comprises the early dialog controllerdetermining the unique identifier by creating said unique identifier orby using a SIP dialog identifier, which is included in the receivedpreliminary response, as a basis for creating said unique identifier.

Optionally, the preliminary message and/or the updating message is anAA-Request, AAR.

Optionally, the method further comprises the early dialog controllerdetermining the unique identifier as a new attribute value pair, AVP,for adding to the AAR, or to extend an existing AVP of the AAR.

Optionally, the updated data comprises data updating the serviceinformation for at least one early dialog.

According to the invention in a third aspect, there is provided acomputer program comprising instructions which, when executed on atleast one processor, cause the at least one processor to carry out themethod above.

According to the invention in a fourth aspect, there is provided acarrier containing the computer program above, wherein the carrier isone of an electronic signal, optical signal, radio signal, ornon-transitory computer readable storage medium.

According to the invention in a fifth aspect, there is provided a nodefor use as a Policy and Charging Rules Function, PCRF. The nodecomprises a receiving means, which may be a receiver, configured toreceive a plurality of preliminary messages from a further node for useas a P-CSCF, wherein each preliminary message corresponds to an earlymedia session to be created by the node and comprises a uniqueidentifier for the early media session. The node comprises an earlymedia session controlling means, which may be an early media sessioncontroller, configured to store the unique identifier in a memory and tocontrol a transmitting means, which may be a transmitter, to transmit apolicy and charging control, PCC, message to a second further node foruse as a Policy and Charging Enforcement Function, PCEF. The receiver isfurther configured to receive an updating message comprising a uniqueidentifier of at least one of the early media sessions and updating datafor updating the at least one early media session. The node furthercomprises an early media session updating means, which may be an earlymedia session updater, configured to identify the at least one earlymedia session based on the received unique identifier in the updatingmessage, and to control the transmitter to transmit an updated PCCmessage comprising the received updating data to the second furthernode.

Optionally, the early media session updater is configured to retrievethe unique identifier from a received message, to review the storedunique identifiers and, if the retrieved unique identifier matches astored unique identifier, to determine that the message is an updatingmessage.

Optionally, the PCC message comprises PCC rules, which may comprise oneor more of: Internet Protocol flows, gate status and Quality of Service.

According to the invention in a sixth aspect, there is provided a methodfor operating a node for use as a Policy and Charging Rules Function,PCRF. The method comprises receiving, by a receiving means, which may bea receiver, a plurality of preliminary messages from a further node foruse as a P-CSCF, wherein each preliminary message corresponds to anearly media session to be created by the node and comprises a uniqueidentifier for the early media session. The method comprises storing, byan early media session controlling means, which may be an early mediasession controller, the unique identifier in a memory. The methodcomprises controlling, by the early media session controller, atransmitting means, which may be a transmitter to transmit a policy andcharging control, PCC, message to a second further node for use as aPolicy and Charging Enforcement Function, PCEF. The method comprisesreceiving, by the receiver, an updating message comprising a uniqueidentifier of at least one of the early media sessions and updating datafor updating the at least one early media session. The method comprisesidentifying, by an early media session updating means, which may be anearly media session updater, the at least one early media session basedon the received unique identifier in the updating message. The methodcomprises controlling, by the early media session updater, thetransmitter to transmit an updated PCC message comprising the receivedupdating data to the second further node.

Optionally, the method further comprises the early media session updaterretrieving the unique identifier from a received message, reviewing thestored unique identifiers and, if the retrieved unique identifiermatches a stored unique identifier, determining that the message is anupdating message.

Optionally, the PCC message comprises PCC rules, which may comprise oneor more of: Internet Protocol flows, gate status and Quality of Service.

According to the invention in a seventh aspect, there is provided acomputer program comprising instructions which, when executed on atleast one processor, cause the at least one processor to carry out themethod above.

According to the invention in a eighth aspect, there is provided acarrier containing the computer program above, wherein the carrier isone of an electronic signal, optical signal, radio signal, ornon-transitory computer readable storage medium.

BRIEF DESCRIPTION OF DRAWINGS

Exemplary embodiments of the invention are disclosed herein withreference to the accompanying drawings, in which:

FIG. 1 is a signalling diagram showing SIP forking policy control in3GPP;

FIG. 2 is an architecture diagram for PCC;

FIG. 3 is a block schematic diagram of a P-CSCF;

FIG. 4 is a block schematic diagram of a PCRF;

FIG. 5 is signalling diagram showing an embodiment of the invention toenhance SIP forking policy control;

FIG. 6 is a signalling diagram showing an embodiment of the invention toenhance SIP forking policy control and applicable when an IMS sessionuses the network ring back tone service;

FIG. 7 is a flow diagram showing a method of operating a P-CSCF; and

FIG. 8 is a flow diagram showing a method of operating a PCRF.

DETAILED DESCRIPTION

The methods and apparatuses disclosed herein provide a new mechanism forthe P-CSCF to modify the session information of a particular preliminaryforking response.

The methods and apparatuses disclosed may use the inclusion of a uniquereference identifier, hereinafter unique identifier (UI), for eachdialog in the case of multiple preliminary responses due to forking. TheP-CSCF may add the unique identifier in the AAR message allowing it toupdate the service information for a particular forking dialog, asopposed to simply set the SIP-Forking-Indication AVP to the valueSEVERAL_DIALOGS. The PCRF then provides the updated information towardsa Policy and Charging Enforcement Function (PCEF) (including servicedata flow filters, QoS information and gating status). As commentedabove, An AA-Request (AAR) message is acknowledged towards the P-CSCFwith an AA-Answer (AAA) message. For the sake of simplicity, AAAmessages are neither further commented throughout this specification norillustrated in any drawing.

The unique identifier that can be used for SIP forking may consist of,or may comprise, for example, one or more of the following.

-   -   An ordinal number assigned by the P-CSCF for each early dialog        in the order of increasing time of arrival of the first        preliminary SIP response (180/183) from each terminating end        point.    -   The SIP dialog identifier, which is contained within SIP        messages    -   Any other unique reference identifier for a particular forked        dialog

In order to maintain backward compatibility it is proposed to add theSIP forking unique identifier in a new AVP called“SIP-Forking-Reference”. Alternatively, the existingSIP-Forking-Indication AVP can be extended with new ordinal values suchas “DIALOG_ONE”, “DIALOG_TWO”, etc.

The architecture that supports Policy and Charging Control functionalityis depicted in FIG. 2. This figure has been taken from TS 23.203(V.12.4.0) that specifies the PCC functionality for the Evolved 3GPPPacket Switched domain, including both 3GPP accesses(GERAN/UTRAN/E-UTRAN) and Non-3GPP accesses.

Referring to FIG. 2, a PCRF 200 is in electrical communication with aPCEF 202 via a Gx interface. The PCRF 200 is also in electricalcommunication with an AF 204 via an Rx interface.

The PCRF 200 is a functional element that encompasses policy controldecision and flow based charging control functionalities. The PCRF 200provides network control regarding the service data flow detection,gating, QoS and flow based charging (except credit management) towardsthe PCEF 202. The PCRF 200 receives session and media relatedinformation from the AF 204 and informs AF 204 of traffic plane events.The PCRF 200 provisions PCC Rules to the PCEF 202 via the Gx referencepoint. The PCRF 200 may inform the PCEF 202 through the use of PCC ruleson the treatment of each service data flow that is under PCC control, inaccordance with the PCRF policy decision(s).

The AF 204 is an element offering applications in which service isdelivered in a different layer (i.e. transport layer) from the one theservice has been requested (i.e. signaling layer), the control of IPbearer resources according to what has been negotiated. One example ofan AF 204 is the P-CSCF of the IMS and, therefore, the terms AF andP-CSCF are used interchangeably herein. The AF 204 communicates with thePCRF 200 to transfer dynamic session information (i.e. description ofthe media to be delivered in the transport layer) and to request accessnetwork information. This communication is performed using the Rxinterface.

The PCEF 202 encompasses service data flow detection (based on thefilters definitions included in the PCC rules), as well as online andoffline charging interactions and policy enforcement. Since the PCEF 202is the system element handling the bearers, this is where the QoS isbeing enforced for the bearer according to the QoS information comingfrom the PCRF 200. This functional entity is located at a Gateway 206(e.g. GGSN in the GPRS case, PGW in the EPS case and PDG in theuntrusted WLAN case). For the cases where Proxy Mobile IP (PMIP) is usedinstead of General Packet Radio Service (GPRS) Tunneling Protocol (GTP)between a Bearer Binding and Event Reporting Function (BBERF) 208 andthe PCEF 202, the bearer control is done in the BBERF instead.

FIG. 3 shows a schematic diagram of a network node 300. The network node300 may be a P-CSCF or AF 204.

The node 300 comprises a transmitter 302 and a receiver 304. Thetransmitter 302 and receiver 304 are in electrical communication withother communication units, nodes, UEs, servers and/or functions in atelecommunications network and are configured to transmit and receivedata accordingly. Transmitter 302 and receiver 304 may be provided witha transceiver, not illustrated in the drawing, for transmitting andreceiving data accordingly.

It is noted that the term “electrical communication” encompasses bothwired and wireless electrical communication. Therefore, electricalcommunication may be, for example, a network communication over a wiredconnection or a network communication of over a radio frequencyconnection.

The node 300 further comprises at least one memory 306 and at least oneprocessor 308. The memory 306 may comprise a non-volatile memory and/ora volatile memory. The memory 306 may have a computer program 310 storedtherein. The computer program 310 may be configured to undertake themethods disclosed herein. The computer program 310 may be loaded in thememory 306 from a non-transitory computer readable medium 312, on whichthe computer program is stored. The processor 308 is configured toundertake at least the functions of an early dialog controller 314 andan updated dialog controller 316, as set out herein.

Each of the transmitter 302 and receiver 304, memory 306, processor 308,early dialog controller 314 and updated dialog controller 316 is inelectrical communication with the other features of the node 300. Thenode 300 can be implemented as a combination of computer hardware andsoftware. In particular, the early dialog controller 314 and updateddialog controller 316 may be implemented as software configured to runon the processor 308. The at least one memory 306 stores the variousprograms or executable files that are implemented by a processor 308,and also provides a storage unit for any required data. The programs orexecutable files stored in the memory 306, and implemented by theprocessor 308, can include the early dialog controller 314 and updateddialog controller 316, but are not limited to such.

FIG. 4 shows a schematic diagram of a network node 400. The network node400 may be a PCRF 200.

The node 400 comprises a transmitter 402 and a receiver 404. Thetransmitter 402 and receiver 404 are in electrical communication withother communication units, nodes, UEs, servers and/or functions in atelecommunications network and are configured to transmit and receivedata accordingly. Transmitter 402 and receiver 404 may be provided witha transceiver, not illustrated in the drawing, for transmitting andreceiving data accordingly.

The node 400 further comprises at least one memory 406 and at least oneprocessor 408. The memory 406 may comprise a non-volatile memory and/ora volatile memory. The memory 406 may have a computer program 410 storedtherein. The computer program 410 may be configured to undertake themethods disclosed herein. The computer program 410 may be loaded in thememory 406 from a non-transitory computer readable medium 412, on whichthe computer program is stored. The processor 408 is configured toundertake at least the functions of an early media session controller414 and an early media session updater 416, as set out herein.

Each of the transmitter 402 and receiver 404, memory 406, processor 408,early media session controller 414 and early media session updater 416is in electrical communication with the other features of the node 400.The node 400 can be implemented as a combination of computer hardwareand software. In particular, the early media session controller 414 andearly media session updater 416 may be implemented as softwareconfigured to run on the processor 408. The at least one memory 406stores the various programs or executable files that are implemented bya processor 408, and also provides a storage unit for any required data.The programs or executable files stored in the memory 406, andimplemented by the processor 408, can include the early media sessioncontroller 414 and early media session updater 416, but are not limitedto such.

FIG. 5 shows the mechanism proposed in the methods and apparatusesdisclosed herein to enhance policy control in SIP forking scenarios. TheP-CSCF 204 provides a unique identifier in a new SIP-Forking-ReferenceAVP when provisioning the service information, which corresponds to afirst preliminary response (step S-501) in a SIP forking scenario, tothe PCRF 200 (step S-505) for a corresponding early media session to becreated at the PCRF. When the P-CSCF 204 receives a subsequent SDPoffer-answer exchange updating service information for a subsequentearly dialogue (step S-508), the P-CSCF 204 can modify the serviceinformation previously provided to the PCRF 200 for this particularforking leg by making use of the same unique identifier in theSIP-Forking-Reference AVP.

This allows the PCRF 200 to modify the PCC rules and IP flows alreadyprovided to the PCEF 202 for this particular forking leg.

Referring to FIG. 5:

-   S-501. A UE initiates a SIP session that is sent to multiple    destinations in the terminating IMS network due to SIP forking. The    UE may do this by sending SIP message to the P-CSCF (AF) 204 through    the gateway 206 of FIG. 2. The P-CSCF 204 receives a first    preliminary response for a first early dialog that includes an SDP    answer payload.-   S-502. The P-CSCF 204 sends corresponding first service information    to the PCRF 200 for the purpose of authorizing the IP flows and the    QoS resources required for the negotiated IMS session. The P-CSCF    204 includes a first unique identifier (UI#1) in the    SIP-Forking-Reference AVP within the AAR message.-   S-503. The PCRF 200 performs session binding, authorizes the service    information and provisions the PCC rules in the PCEF 202.-   S-504. The P-CSCF 204 receives a second preliminary response for a    second (new) early dialogue.-   S-505 The P-CSCF 204 sends an AAR message within the existing    Diameter session containing a second unique identifier (UI#2) in the    SIP-Forking-Reference AVP and including second service information    derived from this second preliminary response.-   S-506. The PCRF 200 identifies the existing authorization    information for the P-CSCF session, and authorizes the maximum    bandwidth required by any of the dialogues identified by the first    and the second unique identifiers.-   S-507 The PCRF 200 updates the PCC rules it previously provided to    the PCEF 202 with additional service data flow filters corresponding    to the second service information and with updated QoS information.-   S-508. The P-CSCF 204 receives a further preliminary response with    an update to the SDP offer-answer exchange within the second early    dialog and updates the second service information previously    provided to the PCRF 200 for this particular forking leg.-   S-509. The P-CSCF 204 sends an AAR message within the existing    Diameter session containing the second unique identifier (UI#2) in    the SIP-Forking-Reference AVP and including the updated second    service information derived from the latest preliminary response.-   S-510. The PCRF 200 can identify that this is a modification of the    session information for a previous preliminary response, e.g. the    second session information, by looking at the value provided in the    SIP-Forking-Reference AVP, e.g. the second unique identifier (UI#2).-   S-511. The PCRF 200 then updates the information provided in the    existing PCC rules towards the PCEF 202 (including updated service    data flow filters, updated QoS information, gating status, etc.).

The methods and apparatuses disclosed herein provide a mechanism for theP-CSCF 204 to update the session information for each subsequent SDPoffer-answer exchange within an early dialog due to SIP forking. TheP-CSCF 204 provides a unique identifier in the SIP-Forking-Reference AVPwhen provisioning the service information of the initial response andfor any additional early media session. The PCRF 200 stores theSIP-Forking-Reference information together with the service informationfor each forking leg.

The P-CSCF 204 can update the service information of a particular earlydialog by using an AAR message within the existing Diameter sessioncontaining the SIP-Forking-Reference AVP with the particular uniqueidentifier for this particular early media session.

If the AAR message contains an existing unique identifier in theSIP-Forking-Reference AVP, the PCRF 200 transmits modified PCC rulesbased on the updated information (e.g. IP flows, gate status, QoS) tothe PCEF 202. The PCEF updates the PCC information previously providedto the PCEF 202 for this particular forking leg.

If an AAR command transmitted to the PCRF 200 contains a new value asunique identifier in the SIP-Forking-Reference AVP, the PCRF 200modifies the PCC rules to include the new service data flow filtersprovided for the new forking leg.

FIG. 6 shows a message flow for the establishment of an IMS call thatincludes the NRBT service generated using the forking model, and QoSpreconditions. Only the originating domain is shown in detail. FIG. 6relates to exemplary methods and apparatuses using a network ring backtone, although the methods and apparatus disclosed herein may be appliedto any scenario using SIP forking. Referring to FIG. 6:

-   -   During steps S-601 and S-602, the user initiates a call. The UE        sends a SIP INVITE requests containing an SDP offer and        requesting for preconditions negotiation. The terminating side        answers with a SIP 183 Session in Progress indicating the media        resources for the remote side.    -   During steps S-603 to S-606, media resource reservation takes        place. The P-CSCF 204 sends (step S-604) an Rx AAR command to        the PCRF 200 to allocate resources in the EPC including media        information for the session. The AAR command includes a first        SIP-Forking-Reference AVP as a unique identifier (Dialog#1) for        a first early dialog. The PCRF 200 associates the received        service data flows to an existing IP Connectivity Access Network        (IP-CAN) session and creates a set of policy rules for the media        negotiated, which triggers the PGW to create a new dedicated        bearer for each media type being negotiated. An example is given        below for possible values in the AAR message session        information. The exemplary IMS session contains a single media        component (AUDIO at 30.5 kbps) with two media sub-components.        Flow number #1 carries the Real-time Transport Protocol (RTP)        data and flow number #2 the Real-time Transport Control Protocol        (RTCP) data.

Session information in AAR message (step S-604) AAR ....... Media-Component-Description Media-Component-Number = 1  Media-Type =AUDIO  Max-Requested-Bandwidth-UL = 30500  Max-Requested-Bandwidth-DL =30500  SIP-Forking-Reference = Dialog#1  Media-Sub-Component Flow-Number= 1 Flow-Status = DISABLED Flow-Description = permit out 17 from10.168.1.98 2252 to 10.168.1.124 37006 Flow-Description = permit in 17from 10.168.1.124 37006 to 10.168.1.98 2252 Flow-Usage = NO_INFORMATION Media-Sub-Component Flow-Number = 2 Flow-Status = ENABLEDFlow-Description = permit out 17 from 10.168.1.98 2253 to 10.168.1.12437007 Flow-Description = permit in 17 from 10.168.1.124 37007 to10.168.1.98 2253 Flow-Usage = RTCP .......

-   -   During the steps S-607 and S-608, the UE detects that        preconditions are met and sends a SIP UPDATE to the remote side.        The remote party answers with a SIP 200 OK for UPDATE.    -   During the steps S-609 to S-612, resources are updated and IP        flows enabled. Resource allocation is updated according to the        last received SDP, and the P-CSCF 204 enables media IP flows to        allow early media by setting the Flow-Status AVP. The P-CSCF 204        sends an Rx AAR command to the PCRF 200 to update the media        information, and the PCRF 200 sends a Gx        Re-Authorization-Request (RAR) message to the PGW 206 in order        to update the PCC rules information. A Re-Authorization-Request        (RAR) message is acknowledged towards the PCRF with a        Re-Authorization-Answer (RAA) message. For the sake of        simplicity, RAA messages are neither further commented        throughout this specification nor illustrated in any drawing.    -   During the step S-613, the remote party stars alerting the        called user and sends a SIP 180 Ringing reply towards the        originating side.    -   During the step S-614, a terminating Multimedia Telephony        Application Server (MTAS) invokes the NRBT service and sends a        forked SIP 183 response back towards the originating UE. The SIP        183 contains a second (new) SIP dialog identifier, includes the        SDP information for the NRBT, and also includes a P-Early-media        header to indicate the authorized early media direction.    -   During the steps S-615 to S-616, resource reservation for ring        back tone starts. The P-CSCF 204, when receiving the forked 183        with early media, sends an AAR with the media information and        additionally, the SIP-Forking-Reference AVP contains a second        unique identifier (Dialog#2) for the second forking leg. An        example is given below for possible values in the AAR message        with session information for NRBT. The NRBT session contains a        single media component (AUDIO at 50 kbps) with two media        sub-components. Flow number #1 carries the RTP data and flow        number #2 the RTCP data. It can be seen that the forking leg        contains a new set of IP flows that need to be authorized by the        PCRF 200 and requires higher bandwidth than the initial resource        reservation in step S-604.

Session information for NRBT in AAR message (step S-616) AAR ....... Media-Component-Description Media-Component-Number = 1  Media-Type =AUDIO  Max-Requested-Bandwidth-UL = 50000  Max-Requested-Bandwidth-DL =50000  SIP-Forking-Reference = Dialog#2  Media-Sub-Component Flow-Number= 1 Flow-Status = DISABLED Flow-Description = permit out 17 from10.168.1.98 2252 to 10.168.1.124 38006 Flow-Description = permit in 17from 10.168.1.124 38006 to 10.168.1.98 2252 Flow-Usage = NO_INFORMATION Media-Sub-Component Flow-Number = 2 Flow-Status = ENABLEDFlow-Description = permit out 17 from 10.168.1.98 2253 to 10.168.1.12438007 Flow-Description = permit in 17 from 10.168.1.124 38007 to10.168.1.98 2253 Flow-Usage = RTCP .......

-   -   During the steps S-617 and S-618, the PCRF updates the        provisioned PCC rules to include additional service data flow        filters for the forked request. Also, if the forked NRBT        response requires higher bandwidth than the first call leg, PCRF        adds the additional bandwidth required to the policy rules.

An example is given below for possible values in the RAR message PCCrule information. The message contains two PCC rules, one for the RTPflow and one for the RTCP flow. The new RTP and RTCP IP flows for thesecond forking leg (NRBT) are added to the PCC rules created for flownumber #1 and flow number #2, respectively.

PCC rule information in RAR message (step S-617) RAR ....... Charging-Rule-Install Charging-Rule-Definition  Charging-Rule-Name =“pcc_rule_name_for_rtp”  Flow-Status = DISABLED  Flow-InformationFlow-Description = permit out 17 from 10.168.1.98 2252 to 10.168.1.12437006  Flow-Information Flow-Description = permit in 17 from10.168.1.124 37006 to 10.168.1.98 2252  Flow-InformationFlow-Description = permit out 17 from 10.168.1.98 2252 to 10.168.1.12438006  Flow-Information Flow-Description = permit in 17 from10.168.1.124 38006 to 10.168.1.98 2252  QoS-InformationQoS-Class-Identifier = QCI_1 Guaranteed-Bitrate-UL = 50000Guaranteed-Bitrate-DL = 50000 Charging-Rule-Definition Charging-Rule-Name = “pcc_rule_name_for_rtcp”  Flow-Status = ENABLED Flow-Information Flow-Description = permit out 17 from 10.168.1.98 2253to 10.168.1.124 37007  Flow-Information Flow-Description = permit in 17from 10.168.1.124 37007 to 10.168.1.98 2253  Flow-InformationFlow-Description = permit out 17 from 10.168.1.98 2253 to 10.168.1.12438007  Flow-Information Flow-Description = permit in 17 from10.168.1.124 38007 to 10.168.1.98 2253  QoS-InformationQoS-Class-Identifier = QCI_1 Guaranteed-Bitrate-UL = 2500Guaranteed-Bitrate-DL = 2500 ........

-   -   During the steps S-619 to S-622, when the UE detects that        preconditions are met for the forking leg, there is another SIP        UPDATE/200 OK negotiation and the P-CSCF 204 sends an Rx AAR        command to the PCRF 200 to update the media information for the        second forking dialog. An example is given below for possible        values in the AAR message with session information update for        NRBT. The AAR message contains the second unique identifier        (Dialog#2) in the SIP-Forking-Reference AVP, together with        updated service information for the RTP (flow number #1) and        RTCP media (flow number #2). The PCRF 200 detects that this        message does not correspond to a new forking leg, but modifies        the service information provided in step S-616 for the NRBT. In        the example, the AAR message enables the IP flow for NRBT.

Session information for NRBT in AAR message (step S-622) AAR ....... Media-Component-Description Media-Component-Number = 1  Media-Type =AUDIO  Max-Requested-Bandwidth-UL = 50000  Max-Requested-Bandwidth-DL =50000  SIP-Forking-Reference = Dialog#2  Media-Sub-Component Flow-Number= 1 Flow-Status = ENABLED Flow-Description = permit out 17 from10.168.1.98 2252 to 10.168.1.124 38006 Flow-Description = permit in 17from 10.168.1.124 38006 to 10.168.1.98 2252 Flow-Usage = NO_INFORMATION Media-Sub-Component Flow-Number = 2 Flow-Status = ENABLEDFlow-Description = permit out 17 from 10.168.1.98 2253 to 10.168.1.12438007 Flow-Description = permit in 17 from 10.168.1.124 38007 to10.168.1.98 2253 Flow-Usage = RTCP .......

-   23-24 During the steps S-623 and S-624, the PCRF 200 then transmits    updated PCC rules to the PCEF 202 and enables the IP flow for NRBT.    The contents of the PCC rule information in the RAR message is shown    below.

PCC rule information in RAR message (step S-623) RAR ....... Charging-Rule-Install Charging-Rule-Definition  Charging-Rule-Name =“pcc_rule_name_for_rtp”  Flow-Status = ENABLED ........

If the AAR message contains the SIP-Forking-Information AVP set toSEVERAL_DIALOGS and no unique identifier, according to the existingfunctionality, the PCRF 200 cannot detect that this is a modification ofthe session information for a previous forking response. The PCRF 200would then update the provisioned PCC rules, as if it were an additionalpreliminary response due to forking, and include additional service dataflow filters in the PCC rule definition. This results in unnecessaryTraffic Flow Template (TFT) filters being installed in the PCEF 202,which trigger Evolved Packet System (EPS) bearer update procedures.

-   -   During the steps S-625 to S-627, the network plays the ring back        tone to the originating terminal. When the terminating side        answers the call, the early dialogue for NRBT is terminated and        the service information is updated to match the requirements of        the final SIP response.

FIG. 7 shows a flow diagram of a method for operating a node (300) foruse as a P-CSCF/AF 204.

The receiver 304 receives 700 a first preliminary response from a firstterminating end point as part of SIP forking. The early dialogcontroller 314 determines 702 a first unique identifier for a firstearly dialog relating to the first preliminary response, as set outabove. The early dialog controller 314 controls the transmitter 302 totransmit 704 a first preliminary message (initial provisioning message)to a PCRF 200 for creating a first early dialog, wherein the firstpreliminary message includes the first unique identifier. The firstpreliminary message may be an initial provisioning message, an AARmessage.

The receiver 304 receives 706 a second preliminary response from asecond terminating end point. The early dialog controller 314 determines708 a second unique identifier for a second early dialog relating to thesecond preliminary response. The early dialog controller 314 controlsthe transmitter 302 to transmit 710 a second preliminary message to thePCRF 200 for creating a second early dialog, wherein the secondpreliminary message includes the second unique identifier. The secondpreliminary message may be an AAR message.

The receiver 304 receives 712 a message comprising updated serviceinformation for the first early dialog. The updated dialog controller316 retrieves the first unique identifier from the updated message andthen retrieves 714 the first unique identifier for the first earlydialog, which has been stored in memory 306 by the early dialogcontroller 314 after being determined. As there is a match, the updateddialog controller 316 is able to determine that the message is anupdating message. The updated dialog controller 316 controls thetransmitter 302 to transmit 716 an updating message to the PCRF 200 forupdating the first early dialog PCC rules, wherein the updating messagecomprises the first unique identifier and updating data, which is basedon the received updated service data. The updating message may be an AARmessage.

FIG. 8 is a flow diagram showing a method for controlling a node 400 foruse as a PCRF 200.

The receiver 404 receives 800 a first preliminary message from theP-CSCF 204 for creating a first early media session. The firstpreliminary message comprises a first unique identifier for the firstearly media session. The early media session controller 414 retrieves802 the first unique identifier from the received message, for example,by extracting it therefrom. The early media session controller 414 maycheck 804 the determined first unique identifier against uniqueidentifiers stored in memory 406 to determine whether the receivedmessage is a new preliminary message or an updating message. As this isthe first message received, this step may be omitted. The early mediasession controller 414 stores 806 the first unique identifier in thememory 406 and controls the transmitter 402 to transmit 808 a first PCCmessage corresponding to the first early media session to the PCEF 202.

The receiver 404 receives 810 a second preliminary message from theP-CSCF 204, corresponding to a second early media session to be createdand comprising a second unique identifier. As before, the early mediasession controller 414 retrieves 812 the second unique identifier fromthe received message and checks 814 the retrieved second uniqueidentifier against unique identifiers stored in memory 406. As this is asecond unique identifier, there is no match so the early media sessioncontroller 414 stores 816 the second unique identifier in memory 406 andcontrols the transmitter 402 to transmit 818 a second PCC messagecorresponding to the second early media session to the PCEF 202.

The receiver 404 receives 820 an updating message from the P-CSCF 204for the first early media session. The updating message comprises thefirst unique identifier and data for updating the first early mediasession. The early media session updater 416 retrieves the first uniqueidentifier from the received updating message and checks 822 it againstthe stored unique identifiers. In this case, there is a match againstthe first unique identifier and the early media session updater 416determines that the message is an updating message for the first earlymedia session rather than a new preliminary message. The early mediasession updater 416 controls the transmitter 402 to transmit 824 anupdating PCC message corresponding to the first early media session andcomprising the first unique identifier and data corresponding to thereceived updated data to the PCEF 202.

A computer program may be configured to provide any of the abovedescribed methods. The computer program may be provided on a computerreadable medium. The computer program may be a computer program product.The product may comprise a non-transitory computer usable storagemedium. The computer program product may have computer-readable programcode embodied in the medium configured to perform the method. Thecomputer program product may be configured to cause at least oneprocessor to perform some or all of the method.

Various methods and apparatus are described herein with reference toblock diagrams or flowchart illustrations of computer-implementedmethods, apparatus (systems and/or devices) and/or computer programproducts. It is understood that a block of the block diagrams and/orflowchart illustrations, and combinations of blocks in the blockdiagrams and/or flowchart illustrations, can be implemented by computerprogram instructions that are performed by one or more computercircuits. These computer program instructions may be provided to aprocessor circuit of a general purpose computer circuit, special purposecomputer circuit, and/or other programmable data processing circuit toproduce a machine, such that the instructions, which execute via theprocessor of the computer and/or other programmable data processingapparatus, transform and control transistors, values stored in memorylocations, and other hardware components within such circuitry toimplement the functions/acts specified in the block diagrams and/orflowchart block or blocks, and thereby create means (functionality)and/or structure for implementing the functions/acts specified in theblock diagrams and/or flowchart block(s).

Computer program instructions may also be stored in a computer-readablemedium that can direct a computer or other programmable data processingapparatus to function in a particular manner, such that the instructionsstored in the computer-readable medium produce an article of manufactureincluding instructions which implement the functions/acts specified inthe block diagrams and/or flowchart block or blocks.

A tangible, non-transitory computer-readable medium may include anelectronic, magnetic, optical, electromagnetic, or semiconductor datastorage system, apparatus, or device. More specific examples of thecomputer-readable medium would include the following: a portablecomputer diskette, a random access memory (RAM) circuit, a read-onlymemory (ROM) circuit, an erasable programmable read-only memory (EPROMor Flash memory) circuit, a portable compact disc read-only memory(CD-ROM), and a portable digital video disc read-only memory(DVD/Blu-ray).

The computer program instructions may also be loaded onto a computerand/or other programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer and/or otherprogrammable apparatus to produce a computer-implemented process suchthat the instructions which execute on the computer or otherprogrammable apparatus provide steps for implementing the functions/actsspecified in the block diagrams and/or flowchart block or blocks.

Accordingly, the invention may be embodied in hardware and/or insoftware (including firmware, resident software, micro-code, etc.) thatruns on a processor, which may collectively be referred to as“circuitry,” “a module” or variants thereof.

It should also be noted that in some alternate implementations, thefunctions/acts noted in the blocks may occur out of the order noted inthe flowcharts. For example, two blocks shown in succession may in factbe executed substantially concurrently or the blocks may sometimes beexecuted in the reverse order, depending upon the functionality/actsinvolved. Moreover, the functionality of a given block of the flowchartsand/or block diagrams may be separated into multiple blocks and/or thefunctionality of two or more blocks of the flowcharts and/or blockdiagrams may be at least partially integrated. Finally, other blocks maybe added/inserted between the blocks that are illustrated.

The methods and apparatus disclosed herein provide new mechanisms forthe P-CSCF 204 to update the session information for each subsequent SDPoffer-answer exchange within an early dialog due to SIP forking.

The following benefits are highlighted:

-   -   Enables the P-CSCF 204 to modify the session information of a        particular early dialog due to SIP forking.    -   Enables the PCRF 200 to perform independent policy control per        early media session due to SIP Forking.    -   In scenarios with CAT or NRBT services, enables the PCRF 200 to        detect that only the flow state is changed, and not all flow        information at an Rx update from P-CSCF 204.    -   Decreases the number of EPS bearer update procedures towards the        UE due to unnecessary updates of the service data flow filters        in the PCC rule definition during SIP forking.    -   Every update bearer request increases the likelihood that the        call setup will fail.    -   Each update bearer request requires a Radio Resource Control        (RRC) reconfiguration, which introduces at least 60 ms extra        delay for the call setup.    -   Each update bearer request increases the chance of race        conditions in the PGW 206.    -   Increases the likelihood for call setup success, and decreases        the dimensioning needs of Evolved Packet Core (EPC) and Radio        Access Network (RAN), in SIP forking scenarios.

The skilled person will be able to envisage other embodiments withoutdeparting from the scope of the appended claims.

The invention claimed is:
 1. A node for use as a Proxy Call SessionControl Function, P-CSCF, in a telecommunications network, the nodecomprising: a receiver configured to receive a plurality of preliminaryresponses originating from a plurality of terminating end points as partof Session Initiation Protocol, SIP, forking; an early dialog controllerconfigured, for each received preliminary response, to determine aunique identifier and to control a transmitter to transmit acorresponding preliminary message comprising the unique identifier to afurther node for use as a Policy and Charging Rules Function, PCRF, forcreating an early dialog by the further node, wherein the receiver isfurther configured to receive updated data for at least one of thepreliminary responses, the node further comprising an updated dialogcontroller configured to retrieve the unique identifier corresponding tothe at least one preliminary response and control the transmitter totransmit an updating message based on the updated data and comprisingthe retrieved unique identifier to the further node for updating thecorresponding early dialog.
 2. The node according to claim 1, whereinthe early dialog controller is configured to determine the uniqueidentifier by creating said unique identifier or by using a SIP dialogidentifier, which is included in the received preliminary response, as abasis for creating said unique identifier.
 3. The node according toclaim 1, wherein the preliminary message and/or the updating message isan AA-Request, AAR.
 4. The node according to claim 3, wherein the earlydialog controller is configured to determine the unique identifier as anew attribute value pair, AVP, for adding to the AAR, or to extend anexisting AVP of the AAR.
 5. The node according to claim 1, wherein theupdated data comprises data updating the service information for atleast one early dialog.
 6. A method for controlling a node for use as aProxy Call Session Control Function, P-CSCF, in a telecommunicationsnetwork, the method comprising: receiving, by a receiver, a plurality ofpreliminary responses originating from a plurality of terminating endpoints as part of Session Initiation Protocol, SIP, forking;determining, by an early dialog controller, for each receivedpreliminary response, a unique identifier; controlling, by the earlydialog controller, a transmitter to transmit a corresponding preliminarymessage comprising the unique identifier to a further node for use as aPolicy and Charging Rules Function, PCRF, for creating an early dialogby the further node; receiving, by the receiver, updated data for atleast one of the preliminary responses; retrieving, by an updated dialogcontroller, the unique identifier corresponding to the at least onepreliminary response; and controlling, by the updated dialog controller,the transmitter to transmit an updating message based on the updateddata and comprising the retrieved unique identifier to the further nodefor updating the corresponding early dialog.
 7. The method according toclaim 6, further comprising the early dialog controller determining theunique identifier by creating said unique identifier or by using a SIPdialog identifier, which is included in the received preliminaryresponse, as a basis for creating said unique identifier.
 8. The methodaccording to claim 6, wherein the preliminary message and/or theupdating message is an AA-Request, AAR.
 9. The method according to claim8, further comprising the early dialog controller determining the uniqueidentifier as a new attribute value pair, AVP, for adding to the AAR, orto extend an existing AVP of the AAR.
 10. The method according to claim6, wherein the updated data comprises data updating the serviceinformation for at least one early dialog.
 11. A non-transitory computerreadable storage medium comprising a computer program comprisinginstructions which, when executed on at least one processor, cause theat least one processor to carry out the method according to claim
 6. 12.A node for use as a Policy and Charging Rules Function, PCRF, the nodecomprising: a receiver configured to receive a plurality of preliminarymessages from a further node for use as a P-CSCF, wherein eachpreliminary message corresponds to an early media session to be createdby the node and comprises a unique identifier for the early mediasession; an early media session controller configured to store theunique identifier in a memory and to control a transmitter to transmit apolicy and charging control, PCC, message to a second further node foruse as a Policy and Charging Enforcement Function, PCEF, wherein thereceiver is further configured to receive an updating message comprisinga unique identifier of at least one of the early media sessions andupdating data for updating the at least one early media session, thenode further comprising an early media session updater configured toidentify the at least one early media session based on the receivedunique identifier in the updating message, and to control thetransmitter to transmit an updated PCC message comprising the receivedupdating data to the second further node.
 13. The node according toclaim 12, wherein the early media session updater is configured toretrieve the unique identifier from a received message, to review thestored unique identifiers and, if the retrieved unique identifiermatches a stored unique identifier, to determine that the message is anupdating message.
 14. The node according to claim 12, wherein the PCCmessage comprises PCC rules, which may comprise one or more of: InternetProtocol flows, gate status and Quality of Service.
 15. A method foroperating a node for use as a Policy and Charging Rules Function, PCRF,the method comprising: receiving, by a receiver, a plurality ofpreliminary messages from a further node for use as a P-CSCF, whereineach preliminary message corresponds to an early media session to becreated by the node and comprises a unique identifier for the earlymedia session; storing, by an early media session controller, the uniqueidentifier in a memory; controlling, by the early media sessioncontroller, a transmitter to transmit a policy and charging control,PCC, message to a second further node for use as a Policy and ChargingEnforcement Function, PCEF; receiving, by the receiver, an updatingmessage comprising a unique identifier of at least one of the earlymedia sessions and updating data for updating the at least one earlymedia session; identifying, by an early media session updater, the atleast one early media session based on the received unique identifier inthe updating message; and controlling, by the early media sessionupdater, the transmitter to transmit an updated PCC message comprisingthe received updating data to the second further node.
 16. The methodaccording to claim 15, further comprising the early media sessionupdater retrieving the unique identifier from a received message,reviewing the stored unique identifiers and, if the retrieved uniqueidentifier matches a stored unique identifier, determining that themessage is an updating message.
 17. The method according to claim 15,wherein the PCC message comprises PCC rules, which may comprise one ormore of: Internet Protocol flows, gate status and Quality of Service.18. A non-transitory computer readable storage medium comprising acomputer program comprising instructions which, when executed on atleast one processor, cause the at least one processor to carry out themethod according to claim 15.